This invention relates to sound absorbing materials. It has particular application to such materials used for aircraft interiors.
Government regulations have been under consideration to establish standards concerning smoke generation and possible limits on toxic thermal decomposition products for aircraft interiors.
Acoustical panels which are composed of, or have a core of sound absorbing material such as fiberglass, mineral wool, or polyurethane form, are well known. None of these materials are used without an exterior skin, and some of the reasons that such an exterior skin is required are:
1. Poor appearance. PA1 2. Degradation due to vibration, heat, moisture, or liquids. PA1 3. Lack of structural integrity. PA1 4. Poor abrasion resistance. PA1 5. Poor acoustical absorption when compressed. PA1 6. Wicking of fluids into the material, constituting a possible fire hazard, or rotting of the material. PA1 7. Deliberate mischief, including many other factors, make it necessary to have a tough abrasion resistant and visually acceptable interior to be combined with a moisture barrier and acoustical material where there are no fibers to break and dust out, causing dermatitis or respiratory problems.
An object of the present invention is to provide a new acoustical panel capable of absorbing sound and attenuating acoustical energy over a wide frequency spectrum that is more efficient in sound absorption than other panels of this general type.
It is a further object to provide a flexible panel which has good abrasion resistance, does not wick liquids, and can be easily handled.
It is also a further objective to provide an acoustical panel that has a good fire rating, does not serve as a fuel and leads to little smoke generation, in addition to having excellent acoustical and mechanical properties as described above.
A further object of the invention is to reduce the amount of toxic thermal decomposition products which may be present in previously used materials.
These objectives are achieved by utilizing a multilayered sound absorbing panel that includes an aramid cloth layer and an aramid felt layer. Such a panel is resistant to breaking of fibers, flame, high temperatures, chemical attack, abrasion, and wicking of fluids. Advantageously, an intervening film between the cloth and felt layers may be included, bonded to those layers in interrupted patterns so as to leave portions of the film non-bonded to those layers. The film may be a polyimide film. The entire panel need not be very thick, with the cloth layer about 0.002 to 0.005 inch thick, the felt layer about 1/8 to 1/2 inch thick, and a very thin polyimide film of about 0.0005 inch thick, to name some representative, non-limiting examples.
The invention will be more completely understood by reference to the following detailed description.